Hydraulic system having means for isolating leaking branch circuits

ABSTRACT

A hydraulic system has a reservoir which contains a hydraulic fluid and includes a piston which bears against that fluid. The system also has a pump which derives fluid from the reservoir and supplies high pressure fluid to a plurality of branch circuits, each having a hydraulic motor or some other hydraulically powered device or load. The branch circuits are connected to the reservoir so that fluid after passing through the hydraulic motors is returned to the reservoir at low pressure. An isolating apparatus is interposed between the pump and branch circuits and includes a main valve for isolating each branch circuit. Each main valve is normally open, and is controlled by a pilot valve which is in turn operated by a cam follower disposed in the path of a cam which is carried by and responsive to the position and movement of the reservoir piston. Should one of the branch circuits develop a leak, the volume of the fluid in the reservoir will decrease, causing the piston to move through the reservoir and carry its cam with it. The cam, by operating the pilot valves associated with the main valves, shuts off and opens the main valves sequentially until the main valve associated with the leaking branch is closed, at which time loss of reservoir fluid terminates and further movement of the piston is merely a function of normal system operating conditions and not leakage. Once operated by the cam the pilot valve for the leaking branch circuit is pressure loaded or mechanically held in a position to isolate the branch from the remainder of the system in which case the pilot valve is independent of cam position.

Thurston 1 June 6, 1972 HYDRAULIC SYSTEM HAVING IVIEANS FOR ISOLATINGLEAKING BRANCH CIRCUITS [72] Inventor: Charles T. Thurston, St. Charles,Mo.

[73] Assignee: McDonnell Douglas Corporation, St.

Louis, Mo.

[22] Filed: Feb. 16, 1971 21 Appl. No.: 115,256

[52] U.S.Cl ..60/5l,60/52 HC,9l/412, 137/411, 244/85 [51] Int. Cl ..FlSbH00 [58] Field of Search ..60/52 HC, 51; 137/411, 395, 137/386; 244/85[56] References Cited UNITED STATES PATENTS 2,396,984 3/1946 Broadstonet al. ..60/52 HC 2,428,150 9/1947 Field ..60/52 l-lC UX 2,574,41611/1951 Rose ..60/52 HC X 2,625,169 1/1953 Parrish ..137/411 X PrimaryExaminer-Edgar W. Geoghegan Atl0rneyGravely, Lieder & Woodruff [57]ABSTRACT A hydraulic system has a reservoir which contains a hydraulicfluid and includes a piston which bears against that fluid. The systemalso has a pump which derives fluid from the reservoir and supplies highpressure fluid to a plurality of branch circuits, each having ahydraulic motor or some other hydraulically powered device or load. Thebranch circuits are connected to the reservoir so that fluid afterpassing through the hydraulic motors is returned to the reservoir at lowpressure. An isolating apparatus is interposed between the pump andbranch circuits and includes a main valve for isolating each branchcircuit. Each main valve is normally open, and is controlled by a pilotvalve which is in turn operated by a cam follower disposed in the pathof a cam which is carried by and responsive to the position and movementof the reservoir piston. Should one of the branch circuits develop aleak, the volume of the fluid in the reservoir will decrease, causingthe piston to move through the reservoir and carry its cam with it. Thecam, by operating the pilot valves associated with the main valves,shuts off and opens the main valves sequentially until the main valveassociated with the leaking branch is closed, at which time loss ofreservoir fluid terminates and further movement of the piston is merelya function of normal system operating conditions and not leakage. Onceoperated by the cam the pilot valve for the leaking branch circuit ispressure loaded or mechanically held in a position to isolate the branchfrom the remainder of the system in which case the pilot valve isindependent of cam position.

1 1 Claims, 6 Drawing Figures PATENTEDJUH 6 I972 SHEET k [If 4 HYDRAULICSYSTEM HAVING MEANS FOR ISOLATING LEAKING BRANCH CIRCUITS BACKGROUND OFTHE INVENTION The invention relates in general to hydraulic systems and,more particularly, to an apparatus for locating and isolating leakingcircuits of hydraulic systems.

Many aircraft of current manufacture utilize hydraulic motors of onetype or another to operate much of the power operated equipment onboard. The use of these motors is not confined to accessories, but isextended to the critical control surfaces which control the flight ofthe aircraft. For example, the stabilator which imparts a pitchingmoment to the aircraft for the purpose of changing elevation is operatedby a hydraulic motor. Likewise so are the ailerons which impart roll tothe aircraft. Similarly, the spoilers which increase drag and reducelift, are also operated by hydraulic motors. The hydraulic motors foroperating the stabilators, ailerons and spoilers form part of a separatehydraulic system within the aircraft, and that system is often termedthe power control system.

Like other hydraulic systems in the aircraft, the power control systemincludes a pump and reservoir, and is a closed loop system in which thereturn to the pump is pressurized above external conditions to preventpump cavitation. Furthermore, the power control system is normallydivided into branch cir cuits in which the stabilators may be on onebranch, the right aileron and right spoiler on another, and the leftaileron and left spoiler on still another. Should anyone of these branchcircuits develop a leak, the hydraulic fluid within the reservoir willeventually be depleted and the entire system will fail, notwithstandingthe fact that only one branch of the system contains a defect. When thisoccurs the pilot must resort to his backup or redundant system whichmost likely is not as sensitive or responsive as the power controlsystem.

Other hydraulic systems on aircraft, such as the utility system whichoperates the landing gear, canopy, and the like, are affected in thesame manner by leaks in their circuits as are hydraulic systems ingeneral.

SUMMARY OF THE INVENTION One of the principle objects of the presentinvention is to provide a multibranch hydraulic system with isolatingmeans for detecting a leak in any of the branches and for isolating thatbranch from the remaining branches so that the remaining branches willnot be rendered inoperative due to complete loss of the system fluid.Another object is to provide isolating means of the type stated whichoperates mechanically and is highly reliable. A further object is toprovide isolating means of the type stated which is not sensitive to andis unaffected by system dynamics, flow transients, pressure surges,thermal expansion and the like. An additional object is to provideisolating means of the type stated which is ideally suited for use inthe power control and other hydraulic systems of aircraft. These andother objects and advantages will become apparent hereinafter.

The present invention is embodied in a hydraulic system having areservoir, a pump, and a plurality of branch circuits. Between thedischarge side of the pump and each branch circuit the system isprovided with isolating means which is responsive to the volume of thefluid in the reservoir and isolates the individual branch circuits asthe fluid volume decreases. The invention also resides in the isolatingmeans. The invention also consists in the parts and in the arrangementsand combinations of parts hereinafter described and claimed.

DESCRIPTION OF THE DRAWINGS In the accompanying drawings which form partof the specification and wherein like numerals refer to like partswherever they occur:

FIG. 1 is a schematic view of a hydraulic system constructed inaccordance with and embodying the present invention;

FIG. 2 is an elevational view, partially broken away and in section,showing a reservoir and an isolating apparatus forming part of thepresent invention;

FIG. 3 is a sectional view taken along lines 3-3 of FIG. 2;

FIGS. 4 and 5 are sectional views taken along lines 4-4 and 5-5,respectively, of FIG. 3; and

FIG. 6 is a sectional view taken along lines 6-6 of FIG. 2.

DETAILED DESCRIPTION branch circuits 8, 10 or 12 and for isolating thebranch circuit in which the leak exists. The pump 6 is connected to thereservoir 4 through a suction line 18 and discharges high pressure fluidinto a high pressure supply line 20 which empties into the isolatingapparatus 16 and further supplies fluid to the reservoir 4 for so-calledbootstrap pressurization. The isolating apparatus 16, in turndistributes the high pressure fluid to the branch circuits 8, l0 and 12,each of which includes a distributor line 22 leading to its hydraulicmotor 14. Each branch cir cuit 8, 10 and 12 further includes a checkvalve 24 through which the hydraulic fluid from its motor 14 passesbefore entering a common return line 26 which is also connected to theisolating apparatus 16 and empties into the reservoir 4, thus completingthe circulation of the'hydraulic fluid. The supply line 20 and returnline 26 are connected through a relief valve The reservoir 4 includes(FIG. 2) acylindrical housing 30 containing an annular type of piston 32which upon movement wipes the inwardly presented cylindrical wall of thereservoir housing 30. The front or lower face of the piston 32, that isthe face presented toward the ports of the suction and return lines 18and 26, bears against the fluid in the reservoir 4, whereas the backface of the piston 32 is for the most part exposed to ambient pressureconditions existing externally of the system 2. Projecting axially fromthe back face of the piston 32 is a hollow piston rod 34, thecylindrical inside face of which is wiped by a fixed piston 36 mountedon a fluid supply tube 38 which extends axially through the center ofthe housing 30. The supply tube 38 projects through the main body of thepiston 32 so that the outside face is wiped by the piston 32. At itsopposite end the supply tube 38 is secured to the housing 30 where it isconnected with the high pressure supply line 20. Near the fixed piston36 the interior of the supply tube 38 communicates with the interior ofthe hollow piston rod 34 through a radial port 40, and this port islocated intermediate the movable piston 32 and the fixed piston 36.Thus, the interior of that much of the piston rod 34 located between thepistons 32 and 36 is at the pressure of the high pressure supply line20, and the high pressure exerts force on a limited area along thebackside of the movable piston 32, that area being annular and locatedbetween the piston rod 34 and the supply tube 38. Accordingly, the highpressure fluid in the piston rod 34 forces the piston 32 downwardly inthe housing 30 against the main body of fluid therein, and thispressurizes the fluid within the housing 30, although not to nearly thepressure of the fluid leaving the discharge port of pump 6. Since thefluid within the housing 30 is pressurized, so is the fluid within thereturn line 26 and suction line 18, and this prevents the pump 6 fromcavitating.

The disposition of the piston rod 34 in the housing 30 is dependent onthe amount of fluid in the housing 30, and should the quantity of fluiddecrease, the piston 32 will move or drop closer to the base of thehousing 30, carrying the piston rod 34 with it. Thus, when a leakdevelops in the system 2, the volume of fluid in the reservoir housing30 will decrease and the piston rod 34 will retract into the housing 30.At its outwardly presented end the piston rod 34 is encircled by aflange-like camming surface 42 which projects radially outwardly fromthe outer surface of the rod 34 and is in effect composed of two beveledsurfaces.

The isolating apparatus 16 includes (FIGS. 3-5) a valve block 44 whichis formed integral with or bolted to the reservoir housing 30 adjacentto the outwardly projecting portion of the piston rod 34. The valveblock 44 contains three main valves 46, 48 and 50 (FIG. 1) which controlthe flow of high pressure fluid to the branch circuits 8, and 12,respectively. Each main valve 46, 48 and 50 (FIGS. 3 and 4) is housedwithin a valve bore 52 formed in the valve block 44, and each valve bore52 near its inner end is surrounded by an annular relief 56 which opensinto a single supply channel 58 (FIG. 4) leading from an inlet port 60.Thus, the supply channel 58 is common to the annular reliefs 56 of allthe valves 46, 48 and 50. The high pressure supply line 20 connects withthe inlet port 60 so that the annular relief 56 of each valve 46, 48 and50 is supplied with high pressure hydraulic fluid. Axially beyond itsannular relief 56 each valve bore 52 is encircled by another annularrelief 62, and the reliefs 62 of the individual valve bores 52,'incontrast to the reliefs 56, are separated from each other and open intoindividual distributor channels 64 (FIG. 3). In other words, the valveblock 50 contains three individual and separate annular reliefs 62, andlikewise three individual and separate distributor channels 64. Thedistributor channels 64 terminate at distributor ports 66, and each port66 is connected to the distributor line 22 of a different branch circuit8, l0 and 12. Finally, near their outer ends the valve bores 52 areencircled by still more annular reliefs 68, and each of these annularreliefs 68 opens into an override channel 70 (FIG. 4) which is common toall of the reliefs 68. Thus, each valve bore 52is surrounded by threeannular reliefs 56, 62 and 68 arranged in that order from the inner endof the valve bore 52.

The main valves 46, 48 and 50 are identical in construction andoperation, and by reason of this fact only the valve 46 associated withthe branch circuit 8 will be described in detail. That main valve 46includes (FIGS. 3 and 4) a valve sleeve 78 and a valve spool 80 which ishoused within the sleeve 78 and is free to shift axially to and frotherein. In one position the valve spool 80 blocks the interior of thevalve sleeve 78 between the annular reliefs 56 and 62, and hence thevalve 46 is considered closed when the spool 80 is so disposed, while inthe opposite position the valve spool 80 allows fluid to flow throughthe interior of the sleeve 78 from the annular relief 56 to the annularrelief 62, and accordingly the valve 46 is considered open when spool 80is disposed in that other position. More specifically, the valve sleeve78 at its innennost end possesses an end cylinder 82 which at its oneend opens into the end of the main valve bore 52 through an end cap 84.At its opposite end the end cylinder 82 opens into an enlarged valvechamber 86 which is disposed inwardly from and is encircled by theannular relief 56 and indeed opens into the annular relief 56 throughradial ports 88 in the sleeve 78. The valve chamber 86 in turn opensinto a reduced intermediate cylinder 90 at a shoulder-like valve seat92. The intermediate cylinder 90 is disposed at the annular relief 62,and intermediate its' ends it empties into the annular relief 62 throughradial ports 94 in the sleeve 78. Beyond the intermediate cylinder 90the valve sleeve 78 is provided with another enlarged chamber 96 whichis disposed at the annular relief 68 and communicates with the annularrelief 68 through radial ports 98 in the sleeve 78. Finally, at itsouter end the sleeve 78 is retained in position by an end cap 79provided with a centrally disposed reduced bore 100 which extends fromthe end of the enlarged chamber 96 to the outer end face of the end cap79.

The valve spool 80 includes (FIGS. 3 and 4) an operating piston 106which is positioned in and engaged with the walls of the end cylinder82, and extending from the piston 106 is a stem 108 which projectsaxially through enlarged valve chamber 86 into which the radial ports 88open. The stem 108 in turn merges into a poppet 110 having a beveledface 112 which moves toward and away from the valve seat 92 when thespool shifts. When the beveled face 112 engages the seat 92 the spool 80is in its closed position, and conversely when the beveled face 112 isaway from the seat 92 the spool 80 is in its open position. At thereduced end of the beveled face 112 the poppet merges into another andlonger stem 114 which extends through the intermediate cylinder 90 tobeyond the radial ports 94 which empty into the annular relief 62 whereit is joined with a return piston 116 which wipes the walls of theintermediate cylinder 90. The piston 116 is at its opposite end engagedby a return shaft 1 18 which extends axially through the enlarged endchamber 96 and is urged toward the valve seat 92 by a coil-typecompression spring 120 which encircles it. The return shaft 118 mergesinto an indicator pin 122 which projects through the reduced bore 100and aligns with an actuator 124 of a limit switch 126 mounted on thevalve block 50 by means of a bracket 128. When the valve spool 80 is inits open position the end of the indicator pin 122 remains spaced fromthe switch actuator 124, but when the spool 80 shifts to its closedposition the indicator pin 122 depresses the switch actuator 124, andthis closes the circuit in which the switch 126 is located.

In addition to the three main valves 46, 48 and 50, the valve block 44further contains three pilot valves 136, 138 and (FIGS. 3 and 5). Thepilot valve 136 operates and is located directly beyond the end of themain valve 46, while the pilot valve 138 operates and is locateddirectly beyond the main valve 48. Similarly, the pilot valve 140 islocated directly beyond and operates the main valve 50. Each pilot valve136, 138 and 140 fits into a pilot valve bore 142 in the valve block 44and the axes of these bores 142 extend radially with respect to the axisof the piston rod 34. Inasmuch as the pilot valves 136, 138 and 140 areidentical in construction and operation, only the pilot valve 136 willbe described in detail.

The pilot valve 136 includes (FIGS. 3 and 5) a valve sleeve 144 whichfits into the pilot valve bore 142 and is retained therein by an end cap145. The valve sleeve 144 has an elongated spool cylinder 146 which atits rear end, that is the end furthest from the piston rod 34, opensinto an enlarged end chamber 147. The spool cylinder 146 is surroundedby three annular reliefs 148, 150 and 152 which exist in the valve block44 or valve sleeve 144 or both. The annular relief 148 opens into thespool cylinder 146 through radial ports 154 and communicates with theinner end of the valve bore 52in which the main valve 46 is contained bymeans of a connecting channel 156 (FIG. 3). The next annular relief 150opens into the midportion of the spool cylinder 146 through radial ports158 and is further connected with the high pressure supply channel 58through a supply duct 160 (FIG. 5). The annular relief 150 similarlyopens into the spool cylinder 146 through apertures 162 and like theannular relief 148 is connected to the inner end of the valve bore 52for the main valve 36, the connection being through an obliqueconnecting duct 164 (FIG. 3). On the other hand, the enlarged endchamber 147 near its juncture with the spool cylinder 146 is surroundedby an annular relief 166 formed in the valve block 44 and the end cap145, and this relief 166 opens into the enlarged end chamber 147 throughradial ports 168. The annular relief 168 further empties into a lowpressure return connecting duct 170 (FIGS. 4 and 5) which in turndischarges into a lower pressure return channel 172 (FIG. 4) located inthe valve block 44 adjacent to the high pressure supply channel 58. Thereturn channel 172 terminates at a discharge port 174 in the block 44and that port 174 is connected to the return line 26. i

The spool cylinder 146 and the enlarged end chamber 147 in the valvesleeve 144 of the pilot valve 136 contain a valve spool 176 (FIGS. 3 and5) which shifts axially between an actuating position in which it allowshigh pressure fluid to flow through the cylinder 146 to the end of themain valve bore 52 of the main valve 46 so as to close the valve 46, toa non-actuating position in which it blocks flow from the spool cylinder146 and does not allow further high pressure fluid to flow to the innerend of the main valve bore 52. In particular, the

valve spool 176 includes a pair of spaced pistons 178 and 180 which wipethe walls of the spool cylinder 146 and are connected by a reducedconnecting rod 182. The length of the rod 182 is such that it spaces thepistons 178 and 180 apart a distance slightly greater than the spacingbetween the radial ports 154 and 158 opening into the annular reliefs148 and 150, respectively. When the pilot valve 136 is in its actuatingposition the radial ports 154 and 158 are located opposite theconnecting rod 182, in which case the pistons 178 and 180 will bedisposed on opposite sides of the radial ports 154 and 158,respectively, thus allowing high pressure fluid to flow from the annularrelief 150 through the spool cylinder 146 to the annular relief 148, andthence through the connecting duct 164 to the main valve bore 52 whereit moves the main valve spool 80 therein to its closed position. Thepiston 178 merges into another rod 184 joined to a stop 186, and thestop 186 is in turn connected with an end rod 188 encircled by a coiledcompression spring 190 which urges the pilot valve spool 176 to itsnon-actuating position. The end rod 188 projects through the end of thevalve sleeve 144, and beyond the rear end face of the sleeve 144 it isfitted with a knob 192.

At the opposite or front end of the valve sleeve 144, the piston 180(FIGS. 3 and 5) merges into a short stern 194 which in turn merges intoan operating rod 196 the diameter of which is smaller than the piston180. The operating rod 196 projects through the end of the sleeve 144and likewise beyond the adjacent face of the valve block 44. Between theoperating rod 196 and the sleeve 144 is a gap which when the pilot valvespool 176 is in its actuating position allows fluid to enter the spoolcylinder 146, providing a force to hold the spool 176 in its actuatedposition.

Bolted against the front face of the valve block. 44, that is againstthe face presented toward the piston rod 34, is an actuating mechanism200 (FIGS. 3, 5 and 6) for successively driving the spools 146 of thepilot valves 136, 138 and 140 inwardly to their actuating positions asthe camming surface 42 on the end of the piston rod 34 passesopposite tothose pilot valves 136, 138 and 140. The actuating mechanism 200includes a base plate 202 having three plunger bores 204 (FIG. 5) whichalign with the front ends of the pilot valve bores 142. The plungerbores 204 receive cam plungers 206 having rearwardly opening sockets 208into which the operating rods 196 of the valve spools 176 are fitted.The cam plungers 206 are attached to the operating rods 196 by setscrews 210. At their forward or outwardly presented ends, the plungers206 are fitted with cross pins 212 on which roller followers 214 arejournaled. When any one of the pilot spools 176 is in its nonactuatingposition, the roller followers 214 associated with that spool 176 willlie in the path of the camming surface 42 on the piston rod 34 so thatwhen the camming surface 42 engages the outwardly projecting rollerfollower 214, it will drive the plunger 206 associated with thatfollower 214 inwardly and move the valve spool 176 connected thereto toits actuating position.

The three valve plungers 206 are arranged in a row (FIGS. 5 and 6), andintermediate the plunger bores 204 into which the plungers 206 fit thebase plate 202 has fulcrum elements 216 secured to it. Mounted on andpivoted aboutthe fulcrum elements 216 are connecting links 218 havingbifurcated ends, the furcations 220 of which extend behind the crosspins 212 at the ends of the cam plungers 206. In this connection, itshould be noted that each cross pin 212 projects beyond the sides of thecam plunger 206 which carries it so that when the furcations 220 swingforwardly with the pivoting of the link 218 on which they are carried,those furcations 220 will engage the cross pin 212 adjacent to them anddrive the cam plunger 206 outwardly. Conversely, when the cammingsurface 42 on the piston rod 34 engages a roller follower 214 and drivesit and its cam plunger 206 inwardly, the furcations 220 located adjacentto the ends of the cross pin 212 on that plunger 206 will be driveninwardly toward the valve block 44, in which case the furcations on theopposite end of the connecting link 218 will be driven outwardly. Thus,when one cam plunger 206 is driven inwardly to a depressed or actuatingposition, the adjacent cam plungers 206 will be forced outwardly totheir withdrawn or non-actuating positions. Where two links 218 areoperated by a single plunger 206, as is the case with the centermostplunger 206, that is the plunger 206 associated with the pilot valve138, the furcations 220 on one of the links 218 are spaced apart adistance sufficient to accommodate the furcations 220 on the other link218 (FIG. 6).

The valve block 44 further contains an override valve 230 (FIG. 4) foroverriding all of the pilot valves 136, 138 and 140 so as to maintaineach main valve 46, 48 and 50 in its open position, irrespective of theposition of the reservoir piston rod 34. The override valve 230 includesa valve sleeve 232 which is fitted into an outwardly opening bore 234 inthe valve block 44 and retained therein by an end cap 235. The sleeve232 is surrounded by five annular reliefs 236, 238, 240, 242 and 244.The center relief 2A0 opens into the override channel 70 leading to theannular reliefs 68 encircling the three main valves 46, 48 and 50. Thetwo end reliefs 236 and 244 are also connected to the override channel70 through ducts 246. The annular relief 242 is connected to the highpressure supply duct leading from the high pressure supply channel 58and accordingly is always maintained at the high or supply pressure. Theremaining annular relief 238, on the other hand, opens into and formsthe upstream end of the low pressure return channel 172 which temiinatesat the discharge port 174 where it empties into the return line 26.Thus, the relief 238 is maintained continually at the low or returnpressure for the system 2.

The override valve sleeve 232 has a spool cylinder 248 and the annularreliefs 238, 240, 242, 244 and 246 communicate with this cylinder 248through radial ports 250 in the sleeve 232. Disposed within the cylinder248 is a spool 252 having two pistons 254 and 256 which are spaced apartby a connecting stern 258. The spool 252 moves axially between anoverride position in which it allows high pressure fluid from theannular relief 242 to pass through the spool cylinder 248 to theoverride channel 70 to a normal position in which the piston 256 blocksthe apertures 250 leading from the annular relief 242 in which the highpressure fluid is contained. More specifically, when the spool 252 is inits normal position, the piston 256 thereon is disposed opposite andcovers the apertures 250 leading from the annular relief 242, while theother piston 254 is positioned intermediate the apertures 250 leading tothe endmost annular relief 236 and the annular 238 located adjacentthereto. In this position, the override channel 70 is vented to thereturn channel 172 and return line 26 through the spool cylinder 248.

The override spool 252 further has an operating rod 260 which extendscompletely through the end of the valve sleeve 232, beyond which it isconnected to a solenoid 262 mounted on the valve block 44. Whenenergized the solenoid 262 draws the spool 252 outwardly to its overrideposition. Within spool cylinder 248 the operating rod 260 is encircledby a coil-type compression spring 264 which urges the override spool 252to its normal position, that is the position in which the apertures 250leading from the annular high pressure I relief 242 are blocked.

The solenoid 262 is wired to an electrical energy source through aswitch 266. Each limit switch 126 is wired in series with warning lamps268, and the limit switches 126 and lamps 268 are likewise placed acrossthe electrical energy source.

OPERATION Normally, the cylindrical housing 30 of the reservoir 4contains enough fluid to position the reservoir piston 32 such that thecamming surface 42 at the end of its piston rod 34 is presented beyondroller follower 214 for the pilot valve 136, which is the pilot valvelocated furthest from the cylindrical housing 30. Thus, all of the pilotvalves 136, 138 and 140 remain in their nonactuating positions, or morespecifically the spools 176 of those valves are urged to theirnonactuating positions by the compression springs 190 therein. The mainvalves 46, 48 and 50, on the other hand, will remain in their openpositions, that is the compression springs 120 therein will urge andmaintain the poppets 110 away from their corresponding seats 92. Themain valves 46, 48 and 50 are primarily held in their open positions bythe differential force resulting from the high pressure fluid in thechamber 86 and low pressure fluid in the bore 52. The override valve230, of course, remains in its normal position, that is the position inwhich the annular reliefs 68 at the enlarged chambers 96 of the mainvalves 46, 48 and 50 are all vented to the return line When the pump 6is energized, high pressure fluid is introduced into the supply line 20,thus causing the pressure in the supply line 20 and likewise the supplytube 38 of the reservoir 4 to rise. This in turn elevates the pressurewithin the hollow piston rod 34 (FIG. 2), creating a force on thebackside of the piston 32. The force so induced pressurizes the mainbody of fluid within the cylindrical reservoir housing 30, although thepressure to which that fluid is elevated is considerably less than thepressure at the discharge side of the pump 6. Since the reservoir fluidis maintained at a pressure greater than the ambient pressure externalto the system, so is the fluid in the suction line 18 and return line 26as well in various cavities and passageways of the valve block 44 whichare connected directly with the return line 26. In aircraft hydraulicsystems the supply pressure is normally about 3,000 psi, while thereturn pressure is normally about 50 psi.

To operate any one of the hydraulic motors 14, a valve (not shown) atthe end of the distributor line 22 (FIG. 1) leading to that motor 14 isopened, allowing fluid to flow to the motor 14. Assuming that the motor14 in the branch circuit 8 is actuated, then fluid will flow from thehigh pressure supply line 20 into the valve block 44 through the inletport 60 therein. Within the valve block 44 the fluid flows through thesupply channel 58 (FIG. 4) to the annular relief 56 of the main valve46. The fluid in the relief 56 in turn flows into the enlarged valvechamber 86 of the valve sleeve 78 through the radial port 88. Since thevalve spool 80 of the main valve 46 is in its open position, the poppet110 will be off or away from the valve seat 92 and high pressure fluidwill flow through the intermediate cylinder 90 to the ports 94 whichopen into the annular relief 62. From the relief 62, the fluid flowsthrough the distributor channel 64 (FIG/3) to the outlet port 66 andthence into the distributor line20 of the branch circuit 8. Afterpassing through the motor 14 and energizing the same, the fluid flowsthrough the check valve 24 and then into the return line 26 throughwhich it is returned to the reservoir 4. The motors 14in the branchcircuits and 12 operate in a similar manner, only the fluid passingthrough them comes from the main valves 48 and 50, respectively.

Should a leak develop in the branch circuit 8, the hydraulic system 2will lose fluid and the volume of fluid in the housing 30 of thereservoir 4 will decrease, causing the piston 32 to move further intothe housing 30. This, of course, causes the piston rod 34 to partiallyretract into the housing 30. In time the forward end of the spoolcylinder 146 in the pilot valve 136, and this increase in pressure actsagainst the forward face of the piston 180 and drives it to its fullyactuated position, in which case the roller follower 214 will leave thecamming sur face 42. As the pilot spool 176 moves it will, of course,cornthe piston 106 and thereby moves the entire spool 80 against boththe force exerted upon it by the compression spring 120 at the oppositeend of the valve bore-52 and the force unbalance resulting from thediflerence in areas between the pistons 116 and 106. The spool 80 shiftsaxially until the beveled face 112 of the poppet 110 engages the valveseat 92, and when this occurs high pressure fluid can no longer flowthrough the intermediate cylinder 90 of the main valve 46. In otherwords, the poppet 1 10 blocks the flow of high pressure fluid from thesupply line 20 and supply channel 58 on one hand to the distributorchannel 64 and distributor line 22 of the branch circuit 8 on the other.

The closing of the main valve 46 isolates the branch circuit 8 and nomore fluid leaks therefrom or from the system 2. Consequently, thevolumn of the fluid in the reservoir 4 decreases no further, except fornormal system operational changes, and the camming surface 42 on thereservoir piston rod 34 remains generally opposite the roller follower214 for the pilot valve 136. The piston rod 34 will move about thispoint as normal system operation demands.

When the branch circuit 8 is isolated a back-up systemmay be utilized tooperate the component normally operated by the hydraulic motor 14 ofthat circuit 8. For example, if the hydraulic system 2 constitutes thepower control system of an aircraft and the motor 14 of the branchcircuit 8 operates the stabilators of that aircraft, a back-up hydraulicsystem (not shown) may be used to operate those stabilators. In anyevent, no further fluid is lost from the reservoir 4 so that theremaining branches 10 and 12 of the hydraulic system 2 remain in thecamming surface 42 will engage the roller follower 214 (FIG. 3) on thecam plunger 206 located at the end of the pilot valve 136, and will urgethat follower 214 and likewise the plunger 206 and spool 176 of thepilot valve 136 inwardly. After the spool 176 moves a short distance inits valve bore 142, its piston 178 will pass beyond the radial ports 154leading to the annular relief 148. When this occurs, high pressure fluidwill flow from the high pressure supply duct 160 (FIG. 5) into theannular relief 150'and thence into the spool cylinder 146 through theradial ports 158. The fluid will further flow through the spool cylinder146 and into the annular relief 148 through the radial ports 154. Fromthe relief 148 the high pressure fluid is directed through theconnecting channel 156 (FIG. 3) to the inner end of the main valve bore52 for the main valve 46. The increase in pressure at the inner end ofthe main valve bore 52 is transmitted through the oblique connectingduct 164, annular relief 152, and radial ports 162 to operation in theusual manner. In other words, a leak in the branch circuit 8, or forthat matter the other branch circuits l0 and 12, will not cause theeventual failure of the entire hydraulic system 2 through the depletionof its hydraulic fluid.

Since the' diversion of high pressure fluid through the obliqueconnecting duct 164 interposed between the main valve 46 and its pilotvalve 136 causes the pilot spool 176 to shift to its fully actuatedposition, in which case the roller follower 214 is away from the cammingsurface 42, the pilot valve 136 once actuated is not sensitive to flowtransients, pressure surges, thermal expansion and the like in thesystem 2. In this connection, it should be noted that the spacingbetween the roller followers 214 of the pilot valves 136, 138, 140, issuch that normal reservoir level changes do not move the piston 32 andcamming surface 42 enough to trip an adjacent pilot valve.

Assuming now that the leak is not in the branch circuit 8, but isinstead in the branch circuit 10, then after the pilot valve 136 ismoved to its actuated position and the main valve 46 associatedtherewith is closed, the hydraulic system 2 will still lose fluid andthe volume of fluid in the reservoir 4 will continue to decrease. Thus,the camming surface 42 after engaging and depressing the roller follower214 at the end of the pilot valve 136 will continue to advance towardthe reservoir 30 and in time will engage and depress the cam follower214 at the end of the next pilot valve 138. This not only has the effectof moving the next pilot valve 138 to its actuating position and therebyclosing the main valve 48 associated therewith, but it also rocks theconnecting link 218 between the cam plungers 206 for the pilot valves136 and 138 (FIG. 5). In other words, the cam surface 42 by driving thecam plunger 206 at the end of the pilot valve 138 inwardly, moves theopposite end of the link 218 outwardly, thereby drawing the cam plunger206 at the end of the pilot valve 136 outwardly and moving the pilotvalve 138 to its non-actuating position. More specifically, as theplunger 206 draws the spool 176 of the pilot valve 136 forwardly throughits spool cylinder 146 the piston 178 thereon eventually comes to aposition between the ports 154 and 158 leading to the annular reliefs148 and 150, respectively. This isolates the inner end of the valve bore52 for the main valve 46 from the high pressure fluid in the supply duct160 and vents the inner end of the valve bore 52 to the lower pressureduct 170 which opens into the enlarged end chamber 147 through annularrelief 166 and radial ports 168. With the decrease in pressure at theinner end of the valve bore 52 for the main valve 46, the spring 120moves the main valve spool 80 back to its open position and allows highpressure fluid to again flow through the spool cylinder 146 to thedistributor channel 64 and thence to the distributor line 22 of thebranch circuit 8. Thus, when the next pilot valve 138 is moved to itsactuating position, the pilot valve 136 will be forced back to itsnonactuating position and will allow the main valve 46 associatedtherewith to return to its open position so as to restore the branchcircuit 8 to normal operation.

Of course, when the pilot valve 138 is in its actuating position and themain valve 48 associated therewith is closed, the branch circuit 10associated therewith will be isolated and no further fluid will leaktherefrom. Consequently, the piston 32 will advance no further into thereservoir housing and the main valve 48 will remain closed while theother main valves 46 and 50 will be open.

Assuming now that both the branch circuits 8 and 10 are free of leaksand that the leak is in the branch circuit 12, then the piston rod 34will continue to retract into the reservoir housing 30 and eventuallyits camming surface 42 will engage and depress the cam follower 214 atthe end of the pilot valve 140. This, of course, moves the pilot valve140 to its actuating position which in turn results in the closure ofthe main valve 50, thereby isolating the branch circuit 12. As the pilotvalve 140 moves to its actuating position, the connecting link 218between the pilot valves 138 and 140 forces the pilot valve 138 to itsnonactuating position, and this allows the spring 120 of the main valve48 to restore that valve to its open position, thus reactivating theformerly isolated branch circuit 10.

Should one desire to open any one of the main valves 46, 48 or 50 ifclosed, he need only close the override switch 266. This energizes thesolenoid 262 which draws the spool 252 (FIG. 4) in the override valve230 to its open position, allowing high pressure fluid to flow from theduct 160 to the annular relief 242 and thence into the spool cylinder248 through the radial ports 250 associated with that relief 242. Thehigh pressure fluid flows from the spool cylinder 248 to the overridechannel 70, and since the override channel 70 communicates with theannular relief 68 of the main valves 46, 48 and 50, the fluid in thosereliefs 68 and likewise in the enlarged chambers 96 will be elevated tothe pressure of the fluid in the high pressure supply line 20. Any valvespool 80 in its closed position will accordingly be driven to its openposition so that all branch circuits will operate off the pump 6 andreservoir 4. If the system 2 constitutes the power control system of anaircraft it may be desirable to override the power control system whenexecuting a critical maneuver such as landing, for the short time duringwhich the formerly closed valve is open and the leaking circuit is inoperation will most likely not deplete the reservoir of its hydraulicfluid.

Similarly, a mechanic who desires to check the operation of the mainvalves 46, 48 and 50 and the pilot valves 136, 138 and 140 can do so bypulling the knobs 192 on the latter outwardly away from the valve block44.

It should be noted that the term hydraulic motor as used herein includesnot only hydraulic cylinders, but also any type of hydraulicallyoperated device or load.

This invention is intended to cover all changes and modifications of theexample of the invention herein chosen for purposes of the disclosurewhich do not constitute departures from the spirit and scope of theinvention.

What is claimed is:

1. A hydraulic system comprising a reservoir having a chamber in which ahydraulic fluid is contained and a member associated with the chamberand bearing against the fluid therein so that the position of the memberrelative to the chamber is dependent on the volume of fluid in thechamber, a plurality of branch circuits connected with the reservoir,each branch circuit having at least one hydraulically powered devicewhich is operated by fluid passing through the branch circuit, means forcausing fluid to flow from the reservoir to the branch circuits,isolating means connected between the reservoir and the branch circuitsand responsive to the position of the member relative to the reservoirchamber for blocking the flow of fluid to the branch circuitsindividually when the volume of the fluid in the chamber decreases andfor isolating a branch circuit having a leak therein, whereby thereservoir will not be depleted of fluid and the remaining branchcircuits will remain operational.

2. A hydraulic system according to claim 1 wherein the means for causingfluid to flow from the reservoir to the branch circuits is a pumplocated between the reservoir and the isolating means; and wherein theisolating means sequentially blocks the branch circuits until a leakingbranch circuit is blocked, at which time the isolating means continuesto block and isolate the leaking branch circuit.

3. A hydraulic system according to claim 2 wherein the isolating meanscomprises a different main valve interposed between each branch circuitand the pump, each main valve having an open position wherein it allowshigh pressure fluid from the pump to flow into the branch circuitassociated therewith and a closed position wherein it blocks the flow offluid to the branch circuit associated therewith, and operating meanspositioned between the reservoir piston and main valves for closing eachmain valve when the member reaches a different position relative to thereservoir chamber.

4. A hydraulic system according to claim 3 wherein the member is apiston in the reservoir chamber; wherein the piston carries a cammingsurface; and wherein the operating means includes cam followers whichare engaged and shifted by the camming surface and operate the mainvalves when shifted.

5. A hydraulic system according to claim 4 wherein the operating meansfurther comprises pilot valves which are operated by the cam followersand control the main valves.

6. A hydraulic system according to claim 3 wherein the operating meansincludes means for opening the preceding main valve when a subsequentmain is closed.

7. A hydraulic system according to claim 4 wherein the cam followers arearranged one after another in the direction of movement for the cammingsurface; and wherein the operating means includes connecting linkspivoted intermediate adjacent cam followers such that when one camfollower is engaged and shifted to close the main valve associatedtherewith, the adjacent cam followers will be moved to and held in aposition in which the main valves associated therewith are open, wherebyonly one branch circuit is isolated at a time.

8. A hydraulic system according to claim 4 wherein the isolating meansfurther comprises override means for holding all of the main valves openirrespective of the position of the reservoir piston.

9. A hydraulic system according to claim 4 wherein high pressure fluiddischarged from the pump is diverted to a limited area on the backsideof the reservoir piston so that the piston is forced against the fluidin the chamber and causes the piston to retract into the chamber as thevolume of reservoir fluid decreases.

10. A hydraulic system comprising a reservoir having a chamber in whicha hydraulic fluid is contained, a pump connected with the reservoir, aplurality of main valves connected to the discharge side of the pump, abranch circuit connected to each main valve and to the reservoir, eachbranch circuit having a hydraulically powered device which is operatedby high pressure hydraulic fluid admitted to the branch circuit throughthe main valve associated therewith, movable means shifting in responseto changes in the volume of the fluid in the reservoir chamber due to aleak in one of the branch circuits, and operating means engageable bythe movable means for closing the main valves individually and insequence as the movable means shifts in response to changes in thereservoir fluid volume and until the main valve associated with theleaking branch circuit is closed, whereby the leaking branch circuit isisolated.

11. An apparatus for locating and isolating leaking branch circuits in amultibranch hydraulic system having a pump and a reservoir connected tothe pump and to the circuit branches and provided with a movable meanswhich bears against the fluid in the reservoir and changes position inresponse to changes in the volume of the fluid in the reservoir so thatthe piston will move as the leaking circuit loses fluid; said apparatuscomprising a main valve interposed between the pump and each branchcircuit and, operating means for movingeach main valve from an openposition wherein it admits high pressure fluid to the branch circuitassociated therewith to a closed position wherein it blocks the flow offluid to and isolates that branch circuit, the operatingmeans beingsequentially engaged and mechanically shifted by the movable means asthe movable means shifis in response to the change of volume of thereservoir fluid, whereby the individual branches are sequentiallyisolated until the leaking circuit is isolated.

ll 4 IF i i

1. A hydraulic system comprising a reservoir having a chamber in which ahydraulic fluid is contained and a member associated with the chamberand bearing against the fluid therein so that the position of the memberrelative to the chamber is dependent on the volume of fluid in thechamber, a plurality of branch circuits connected with the reservoir,each branch circuit having at least one hydraulically powered devicewhich is operated by fluid passing through the branch circuit, means forcausing fluid to flow from the reservoir to the branch circuits,isolating means connected between the reservoir and the branch circuitsand responsive to the position of the member relative to the reservoirchamber for blocking the flow of fluid to the branch circuitsindividually when the volume of the fluid in the chamber decreases andfor isolating a branch circuit having a leak therein, whereby thereservoir will not be depleted of fluid and the remaining branchcircuits will remain operational.
 2. A hydraulic system according toclaim 1 wherein the means for causing fluid to flow from the reservoirto the branch circuits is a pump located between the reservoir and theisolating means; and wherein the isolating means sequentially blocks thebranch circuits until a leaking branch circuit is blocked, at which timethe isolating means continues to block and isolate the leaking branchcircuit.
 3. A hydraulic system according to claim 2 wherein theisolating means comprises a different main valve interposed between eachbranch circuit and the pump, each main valve having an open positionwherein it allows high pressure fluid from the pump to flow into thebranch circuit associated therewith and a closed position wherein itblocks the flow of fluid to the branch circuit associated therewith, andoperating means positioned between the reservoir piston and main valvesfor closing each main valve when the member reaches a different positionrelative to the reservoir chamber.
 4. A hydraulic system according toclaim 3 wherein the member is a piston in the reservoir chamber; whereinthe piston carries a camming surface; and wherein the operating meansincludes cam followers which are engaged and shifted by the cammingsurface and operate the main valves when shifted.
 5. A hydraulic systemaccording to claim 4 wherein the operating means further comprises pilotvalves which are operated by the cam followers and control the mainvalves.
 6. A hydraulic system according to claim 3 wherein the operatingmeans includes means for opening the preceding main valve when asubsequent main is closed.
 7. A hydraulic system according to claim 4wherein the cam followers are arranged one after another in thedirection of movement for the camming surface; and wherein the operatingmeans includes connecting links pivoted intermediate adjacent camfollowers such that when one cam follower is engaged and shifted toclose the main valve associated therewith, the adjacent cam followerswill be moved to and held in a position in which the main valvesassociated therewith are open, whereby only one branch circuit isisolated at a time.
 8. A hydraulic systeM according to claim 4 whereinthe isolating means further comprises override means for holding all ofthe main valves open irrespective of the position of the reservoirpiston.
 9. A hydraulic system according to claim 4 wherein high pressurefluid discharged from the pump is diverted to a limited area on thebackside of the reservoir piston so that the piston is forced againstthe fluid in the chamber and causes the piston to retract into thechamber as the volume of reservoir fluid decreases.
 10. A hydraulicsystem comprising a reservoir having a chamber in which a hydraulicfluid is contained, a pump connected with the reservoir, a plurality ofmain valves connected to the discharge side of the pump, a branchcircuit connected to each main valve and to the reservoir, each branchcircuit having a hydraulically powered device which is operated by highpressure hydraulic fluid admitted to the branch circuit through the mainvalve associated therewith, movable means shifting in response tochanges in the volume of the fluid in the reservoir chamber due to aleak in one of the branch circuits, and operating means engageable bythe movable means for closing the main valves individually and insequence as the movable means shifts in response to changes in thereservoir fluid volume and until the main valve associated with theleaking branch circuit is closed, whereby the leaking branch circuit isisolated.
 11. An apparatus for locating and isolating leaking branchcircuits in a multibranch hydraulic system having a pump and a reservoirconnected to the pump and to the circuit branches and provided with amovable means which bears against the fluid in the reservoir and changesposition in response to changes in the volume of the fluid in thereservoir so that the piston will move as the leaking circuit losesfluid; said apparatus comprising a main valve interposed between thepump and each branch circuit and, operating means for moving each mainvalve from an open position wherein it admits high pressure fluid to thebranch circuit associated therewith to a closed position wherein itblocks the flow of fluid to and isolates that branch circuit, theoperating means being sequentially engaged and mechanically shifted bythe movable means as the movable means shifts in response to the changeof volume of the reservoir fluid, whereby the individual branches aresequentially isolated until the leaking circuit is isolated.